1. Technical Field
The present invention relates to a propagation delay time adjustment method, a propagation delay time adjustment system, a propagation delay time adjustment device, a storage medium stored with a propagation delay time adjustment program, and a node device. The present invention is, for example, applicable as a method for performing time adjustment in a reception circuit in a first side communication device in an access network employing synchronous CDM (Code Division Multiplexing).
2. Related Art
Access network systems employing Code Division Multiplexing (CDM) are capable of multiplexing plural transmission signals with the same clock time, and have the characteristics of being able to perform data communication with large amounts of data, while also saving on communication resources, such as frequencies, time slots and the like.
In particular, in so-called synchronous types of CDM, the phase of coded signals that have been coded with different codes must be made to match. This is called code synchronization.
An access network system performs communication between a single exchange side device and N individual subscriber devices. Usually the transmission path lengths between the exchange side device and the respective subscriber side devices are different from each other. Therefore, in order to perform code synchronization (called uplink synchronization) in uplink communication (communication from the subscriber side toward the exchange side), an operation (called ranging) is required to correct misalignment in phase occurring due to the differences in transmission path length.
A method of performing such ranging is described in Japanese Patent Application Laid-Open (JP-A) No. 2007-158585. The ranging method described in JP-A No. 2007-158585 is the following technique.
In a 1-to-N communications system, a center node (exchange side device) fixes the reception phase during ranging processing. Then a transmission permission signal in which the transmission phase is indicated is repeatedly transmitted to the edge node device (subscriber side device) that is to be subjected to synchronization establishment, with the transmission phase changed in the transmission permission signal on each of the repetitions. The edge node device, when it has received the transmission permission signal, transmits a transmission signal for use in synchronization establishment, the transmission signal including a fixed signal, at the transmission phase incorporated within the received transmission permission signal.
Then center node device then determines whether or not the signal of this transmission phase has been validly received, based on a spreading demodulation output signal for a fixed signal period in the signal received from the edge node device, determines the optimum transmission phase of valid reception within an oscillated range of the transmission phase, and notifies this to the edge node device. This is a technique that, by the above, the edge node device sets the transmission phase to this optimum transmission phase when the edge node device has received the optimum transmission phase.
As stated above, since each of the transmission path distances between the exchange side device and the respective subscriber side devices are different, a difference in the transmission time of the transmission signals occurs. Consequently, it is necessary for the difference in transmission time of the transmission signals to be corrected by the above ranging processing.
However, in carrying out the above ranging processing, in order to realize a state in which all of the transmission signals for each of the respective channels are aligned (code synchronization), the following two conditions must first be satisfied.
Condition 1: the difference in the transmission time from the divider 49 in the exchange side device 2 to the gate section 45-n in each of the reception sections 40-n (called the reception skew) being zero (see FIG. 3 and FIG. 4 of JP-A No. 2007-158585).
Condition 2: the difference in the transmission time from the clock generator 44 to the gate section 45-n in each of the reception sections 40-n (called the mail clock skew) being zero (see FIG. 4 of JP-A No. 2007-158585).
Skew is simply used as a collective term for this reception skew and main clock skew. This skew is inherent to the reception configuration of the exchange side device 2.
Consequently, in order to make this skew zero, for example, adoption could be considered of a configuration in which a skew adjustment signal generator that generates a skew adjustment signal is disposed in the exchange side device 2 and the skew adjustment signal is input to the divider 49, so as to adjust the skew by identifying the transmission time difference of each of the channels. By so doing, the skew can be adjusted at the exchange side device 2 alone.
However, since the skew of each of the respective reception sections 40-n needs to be adjusted, an extremely complicated configuration is required with provision of many components, and constructing such an exchange side device 2 is extremely difficult.
Therefore, a propagation delay time adjustment method, a propagation delay time adjustment system, a propagation delay time adjustment device, a storage medium stored with a propagation delay time adjustment program, and a node device are desired that can, by employing a conventional device configuration and network configuration, adjust the skew and establish code synchronization with certainty.